RU2199113C1 - Facility estimating concentration of combustible gases in oxygen-containing atmosphere - Google Patents

Abstract

FIELD: analysis of gaseous atmosphere. SUBSTANCE: facility estimating concentration of combustible gases in oxygen- carrying atmosphere is intended, for instance, for production areas of petroleum and petroleum refining plants, of thermal power plants, of chemical plants and so on to prevent potential explosion-risky situations. Technical result of invention lies in increased accuracy of determination of concentration of combustible gases in oxygencontaining atmosphere by maintaining value of current pulse of generator in specified limits, in securing possibility of supply of pulses of different configuration to thermal catalytic element and in estimation of concentration of individual substances with different physical-chemical properties by that. Facility estimating concentration of combustible gases in oxygen-containing atmosphere includes thermal catalytic element which output is connected to first input of controller which first output is connected to information display and which second output is connected to input of generator whose output is connected to input of thermal catalytic element. Output of generator is connected to input of thermal catalytic element through resistor which resistance R_el lies in limits from 0.5 to 1000 Ohm and to second input controller. EFFECT: increased accuracy of determination of concentration of combustible gases in oxygencontaining atmosphere. 1 dwg

Description

 The invention relates to the field of analysis of gaseous media and can be used to determine the concentration in an oxygen-containing medium, for example, in the working rooms of oil producing and oil refining enterprises, thermal energy enterprises, chemical plants, etc. to prevent situations that are dangerous in relation to the possibility of an explosion.

 A device for determining the concentration of combustible gases in an oxygen-containing medium, comprising a catalytically active sensing element (SE) connected in series with a passive compensation element identical to the SE in thermophysical parameters; by adjusting the supply current in the serial circuit of the sensing and compensation elements, the temperature of the compensation element is kept constant, see. St. USSR 1286985 dated 02/08/1985 according to class. G 01 N 27/16.

 In this device, both elements operate continuously, which leads to high power consumption. The presence of mechanical modulation of the light emitted by the SE and the compensation element, by means of an electric motor with a shutter, leads to additional energy consumption and reduces the reliability of the structure; In addition, constant purging of the reaction chamber is required, and light insulation is also required.

 Also known is a device for determining the concentration of combustible gases in an oxygen-containing medium, including a thermocatalytic element (TCE), placed in a measuring chamber containing the analyzed gas mixture; current pulses are fed to the TCE, heating it to a predetermined temperature and reducing the pulse duration until the initial temperature value is established (see ed. St. USSR 1711061 of 03/10/1989 according to class G 01 N 27/16).

 This device is simpler and allows you to slightly reduce power consumption compared to the device by author. St. USSR 1286985. However, its very serious drawback is the supply of heating pulses in thermal shock mode, which leads to an accelerated TKE failure; in addition, the thermal shock heating mode of the TCE causes almost instantaneous formation of a heated gas boundary layer around the TEC, which leads to a significant change in the steepness of the calibration characteristics of the output signal of the TEC depending on the concentration of combustible gases, expressed as a percentage of the lower concentration limit of flame propagation (% LEL ), with different molecular weights of the combustible gases being analyzed. This variation in the steepness values of these characteristics can be explained by the fact that in the heated gas boundary layer around the TCE, catalytically active substances are formed, which are the decomposition products of the analyzed combustible gas; these substances cause the rapid oxidation of some of the analyzed combustible gases out of contact with the surface of the TCE, which leads to the loss of heat of the TCE and, consequently, to a decrease in the output signal from the TCE. Thus, the device can be used to determine% NKPRP only any one combustible gas in an oxygen-containing medium. This circumstance is not unique to the device according to ed. St. USSR 1711061, but also to all other known devices for determining the concentration of combustible gases in an oxygen-containing medium using TCE, see, for example, V.N. Tarasovich, Metal thermistor converters of combustible gases. - Kiev: Naukova Dumka, 1988, p. 209-210. As can be seen from Fig. 63 on p. 210, there is a very large variation in the steepness of the static characteristics of the output signal of the thermocatalytic element in the case of analysis of gases with different molecular weights. All modern gas analyzers are calibrated for one specific combustible gas (usually methane). To determine the concentrations of other combustible gases, it is necessary to change the sensitivity of the gas analyzer or to recalculate. The determination of the integral explosiveness of multicomponent gaseous media, including combustible components that differ significantly in molecular weight, using known devices is impossible. In addition, among the disadvantages of the device according to ed. St. The USSR 1711061 dated 03/10/1989 refers to the fact that it contains at least two TCEs operating in a continuous diet; this does not allow the creation of portable devices with long continuous operation time. For example, the continuous operation time of the SGG-4M gas analyzer (Russia) with overall dimensions of 150x55x188 mm and a weight of 1.8 kg is 4-8 hours, and the methane gas analyzer GP-82 (Japan) with overall dimensions of 78x142x26 mm and a weight of 310 g - no more 6 o'clock.

 A device for determining the concentration of combustible gases in an oxygen-containing medium, including a thermocatalytic element placed in the measuring chamber, a generator, a controller and an information display unit, the output of the thermocatalytic element is connected to the first output of the controller, the first output of which is connected to the information display unit, and the second output connected to the input of the generator, the output of which is connected to the input of the thermocatalytic element, see, for example, patent of the Russian Federation 2156972.

 This device is taken as a prototype of the present invention. It provides the ability to determine the integral explosiveness of gaseous media, including several components that differ significantly in their molecular weight, eliminates the need to heat TKE in shock mode to a temperature above the catalyst activation temperature and thereby extend the life of TCE. The device uses only one TCE, which eliminates the need for a continuous diet. However, the disadvantage of the prototype is the lack of maintaining the magnitude of the current pulse generated by the generator with the required accuracy, which leads to measurement error. The current pulse generated by the generator is supplied to the TEC, which during the measurement process changes its resistance, which leads to interference and distortion of the current pulse.

 In addition, the disadvantage of the device adopted as a prototype is the impossibility of creating current pulses of various configurations on the TEC, which is necessary to determine the concentration of individual substances with different physicochemical characteristics, for example, carbon monoxide and methane or carbon monoxide and hydrogen, etc.

 The present invention is based on solving the problem of increasing the accuracy of determining the concentration of combustible gases in an oxygen-containing medium by ensuring that the current pulse of the generator is maintained within specified limits, as well as providing the possibility of applying pulses of various configurations to the TCE and thereby determining the concentration of individual substances with different physicochemical properties .

This problem is solved due to the fact that in the device for determining the concentration of combustible gases in an oxygen-containing medium, including a thermocatalytic element located in the measuring chamber, a generator, a controller and an information display unit, the output of the thermocatalytic element is connected to the first input of the controller, the first output of which is connected with the information display unit, and the second output is connected to the input of the generator, the output of which is connected to the input of the thermocatalytic element, according to the invention, the output of the nerator is connected to the input of the thermocatalytic element through a resistor, the resistance R _{e of} which is in the range from 0.5 to 1000 Ohms, while the output of the generator is additionally connected to the second input of the controller.

 The applicant has not identified any technical solutions identical to the claimed invention, which allows us to conclude that it meets the criterion of "novelty" (N).

The implementation of the differences of the claimed invention (in combination with the characteristics indicated in the restrictive part of the claims) leads to important new properties of the subject invention:
- maintaining the magnitude of the current pulse with an accuracy of ± 0.05 mA and thereby reducing the error in determining the concentration of combustible gases in an oxygen-containing medium;
- the possibility of creating current pulses of various configurations on the TEC, which allows us to simultaneously determine the concentration of combustible substances with various physicochemical properties in an oxygen-containing medium.

 These circumstances determine, according to the applicant, the compliance of the claimed technical solution with the criterion of "inventive step" (IS).

 The invention is illustrated in the drawing, which shows a block diagram of the claimed device.

The device includes a thermocatalytic element 1, which is placed in the measuring chamber 2, made in a specific example in the form of a mesh housing. The chamber has the same gas concentration as in the environment. Generator 3 in a specific example is made on chips MAX757, AD8031 and transistor 2TC622. Electric current pulses are supplied from the generator 3 to the TCE 1. The controller 4, in the specific example the 12-bit ADUC812BS, serves to control the generator 3. The information display unit 5 is a display L1672. The output of the TCE 1 is connected to the first input of the controller 4, the first output of which is connected to the information display unit 5, and the second output is connected to the input of the generator, the output of which is connected to the input of the TCE; the output of the generator 3 is connected to the input of the TCE 1 through a resistor 6, the resistance R _{e of} which is in the range from 0.5 to 1000 Ohms, the output of the generator 3 is additionally connected to the second input of the controller 4.

 The device operates as follows. As an example, the simultaneous determination of the concentrations of carbon monoxide and methane in an oxygen-containing medium is considered.

этот коэффициент определяют однократно, он отражает свойства конкретного ТКЭ: омическое сопротивление и геометрические размеры.On TKE 1 serves a pulse of electric current, for example, a sawtooth shape. Preliminarily measure the resistance value Rτ _0-1 TCE at a time in the range from τ ₀ to τ ₁ .. Moreover, τ ₀ is the time before the start of the electric current impulse to the TCE, τ ₁ is the time before the oxidation of combustible gases to TCE surfaces. The resistance value R _{τ1-2 of the} TCE is also preliminarily measured at a time in the range from τ ₁ to τ ₂ , where τ ₂ is the time before the formation of a heated gas boundary layer around the TCE; at this moment, the electric current impulse to the TCE is stopped. Having previously determined Rτ _0-1 and Rτ _1-2 , a constant coefficient is determined

this coefficient is determined once, it reflects the properties of a specific TCE: ohmic resistance and geometric dimensions.

- момент времени, соответствующий началу следующего импульса.When configuring the controller, the values of this coefficient are entered into it, as well as the values of τ ₁ , τ ₂ and τ ₃ , where τ _{3 is the} instant of switching off the current pulse, and at times τ ₂ and τ ₃ , the concentrations of carbon monoxide and methane are determined, respectively. Also set

is the moment of time corresponding to the beginning of the next impulse.

ТКЭ в момент времени τ₂, которое соответствует отсутствию в кислородосодержащей среде оксида углерода и

Эти вычисления осуществляются в контроллере 4. Величина ΔRτ₂ прямо пропорциональна концентрации С оксида углерода в камере 1 и, соответственно, в анализируемой окружающей среде. Значение С отображается на дисплее 5. Затем определяют значение сопротивления R₃ = K₂•Rτ₁ ТКЭ в момент времени τ₃, которое соответствует отсутствию в кислородосодержащей среде метана и

Эти вычисления осуществляются в контроллере 4. Величина ΔR_τ3 прямо пропорциональна концентрации С метана в камере 1 и, соответственно, в анализируемой окружающей среде. Значение С отображается на дисплее 5.Next, determine the current value of the resistance R _τ1 TCE at the time point τ ₁ , as well as the current value of the resistance R _τ2 TCE at the time point τ ₂ and the resistance value R _τ3 at the time point τ ₃ . After that, determine the value of resistance

TCE at time τ ₂ , which corresponds to the absence of carbon monoxide in the oxygen-containing medium and

These calculations are performed in the controller 4. The value of ΔRτ _{2 is} directly proportional to the concentration of carbon monoxide C in the chamber 1 and, accordingly, in the analyzed environment. The value C is displayed on the display 5. Then, the resistance value R ₃ = K ₂ • Rτ ₁ TCE is determined at time τ ₃ , which corresponds to the absence of methane in the oxygen-containing medium and

These calculations are carried out in the controller 4. The value ΔR _{τ3 is} directly proportional to the concentration C of methane in chamber 1 and, accordingly, in the analyzed environment. The value C is shown on display 5.

In the case of a change in the temperature of the oxygen-containing medium over a wide range (from -70 ^o С to + 70 ^o С), it becomes necessary to compensate for the effect of this change on the value of the coefficient K. For this, a number of K values are experimentally determined at various temperatures in the above range. In a specific example, the values of the coefficient K were determined at temperatures: -70 ^° C, -55 ^° C, -20 ^° C, 0 ^° C, +20 ^° C, +45 ^° C, + 70 ^° C. The obtained values of the coefficient K were then approximated. straight line and determined the correction factor β equal to the tangent of the angle of inclination of this straight line, then determined the value
R $\genfrac{}{}{0ex}{}{\text{0t1-2}}{\text{τ2}}$ = [K ^tc + (R $\genfrac{}{}{0ex}{}{\text{tc}}{\text{τ1}}$ -R $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ1}}$ ) β] R $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ1}}$ ,
where r $\genfrac{}{}{0ex}{}{\text{0t1-2}}{\text{τ2}}$ - the calculated value of the resistance of the thermoelectric element at the time τ ₂ in the temperature range from - 70 ^o C to + 70 ^o C;
K ^tc - the value of the coefficient K at a selected constant temperature from the range from - 70 ^o C to + 70 ^o C;
R $\genfrac{}{}{0ex}{}{\text{tc}}{\text{τ1 /}}$ - the value of the resistance of the TCE at time τ ₁ at a selected constant temperature in the range from - 70 ^o C to + 70 ^o C;
R $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ1}}$ - the value of the resistance of the TCE at time τ ₁ in the temperature range from - 70 ^o C to + 70 ^o C;
β is the correction factor.

Next, determine the value
ΔR $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ2}}$ = ΔR $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ2}}$ -ΔR $\genfrac{}{}{0ex}{}{\text{0t1-2}}{\text{τ2}}$ ,
where ΔR $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ2}}$ - the magnitude of the increment of the resistance of TCE at time τ ₂ due to the oxidation reaction;
R $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ2}}$ - the measured value of the resistance of the TCE at time τ ₂ , and in magnitude ΔR $\genfrac{}{}{0ex}{}{\text{t1-2}}{\text{τ2}}$ judge the concentration of carbon monoxide in an oxygen-containing medium at temperatures varying from -70 ^o C to + 70 ^o C.

Similarly determine ΔR $\genfrac{}{}{0ex}{}{\text{t1-3}}{\text{τ3}}$ and the value of the increment of resistance is judged on the concentration of methane in an oxygen-containing medium at temperatures ranging from -70 ^o C to + 70 ^o C.

 The U-shaped current pulse used in the prototype does not allow the determination of substances that are different in their physicochemical properties during the measurement process due to the rapid change in resistance at the initial portion of the transition characteristic.

 The inventive device allows for one measurement cycle using the controller to simultaneously determine the concentration of substances that differ in their physicochemical properties, as well as the total explosion hazard. The problem is solved in a similar way when using current pulses of exponential, step and other forms.

 To implement the claimed device uses the usual simple element base and standard assembly equipment, which allows us to conclude that the invention meets the criterion of "industrial applicability".

Claims (1)

A device for determining the concentration of combustible gases in an oxygen-containing medium, including a thermocatalytic element located in the measuring chamber, a generator, a controller and an information display unit, the output of the thermocatalytic element being connected to the first input of the controller, the first output of which is connected to the information display unit, and the second output is connected with the input of the generator, the output of which is connected to the input of the thermocatalytic element, characterized in that the output of the generator is connected to the input of the thermocat iticheskogo element via a resistor, whose resistance R _e is in the range from 0.5 to 1000 ohms, the output of the generator is further coupled to a second input of the controller.